I just bought a '86 T/A off the internet and got totally screwed on the deal. One of the few things salvagable on the car is a disc brake rear end. I want to put the rear in my '88 T/A. I did a search but didn't come up with much in changing out to a stock model disc rear end. Also, what is part availability on these things? Is it possible to get new or rebuilt calipers? I know I'm going to need them. Thanks for the help.

 

Take everything off the parts car.

You'll want the master cylinder, proportioning valve, lines if possible, emergency brake cable, etc. everything.

However, before you swap- check the gear ratios in your car and in the parts car. are they the same? Is one a limited slip differential? Ids the parts car differntial any good (pull the inspection plate cover off nad check the gear. also check for leaks and bearing play. install new fluid/ gasket) I'd figure that out before you swap for the sake of having discs.

If the gear ratio is different than you need to get a new gear for your trans to keep your speedometer accurate.

Assuming it's all good then you need to change the other parts over aside from the rear axle. Drum brakes work differntly than discs so the fbrake fluid volume/ pressure requirement is different, too. Thsisi why you need to swap these parts over.

And remembe,r many of the third gen brake line fittings are metric. Get the right metric flare wrenches or be ready to replace parts.

 

thanks for the info. Looks like I got a little work ahead of me.

 

oh ****, don't tell me you started all that..... ok, 1st thing.... if it isn't the PBR aluminum calipers like the 4th gens have, pass on it all together. second, instead of remove all the parts and ****, if the diff you have is better than the one on the car (meaning you have posi and the new one does not) or your gear ratio is better, than pull the axles and brakes and swap them. if not, if the nw rear has better stuff, it's much simpler and easier to swap the whole housing brakes and all. just change the e-brake cables (assuming the ones off of the '86 are no good. if they're ok, swap them too).

2nd, the master cylindrs are the same from dsic to drum rears. your drum MC will operate the discs no problem, and so will the stock proportional valve. just either swap axles brakes, and rubber hoses, or swap the whole housing. that's all you need.

 

Unless they were swapped in, an 86 wouldn't have PBR's. As a side note, before I swapped to PBR's, I used the 'fix' kit on the old iron Deco-Moraine's and the brakes worked fine. Generally, I think they're underrated.

JamesC

 

I guess there are some things about this I still don't understand. What are PBR's? So maybe changing out the guts of the brakes will be easier? Will I be able to mount all of the hardware to the drum rearend easily? Will I have to do some adjusting to the proportioning valve? Is it adjustable. I thought I had this all figured out. I'm glad I asked. Thanks for the help.

 

PBR's are finned alum calipers on 11.7 inch rotors. You could put these bigger brakes on the disc rear end without difficulty. Check this link for more info:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

You can't mount the disc brakes to a drum rear without modding the axel flanges. Check this link for the general idea:

https://www.thirdgen.org/ls1reardisc

The proportioning valve is not adjustable.

JamesC

 

flyitlikustolit- I disagree with you. At least on the earlier third gens- the master cylinders have different part numbers between the drum rear and disc rear. If they're the same then why would htey run 2 different part numbers? I bought one this last weekend so it's fresh in my memory. His car is only 2 years newer than mine- so it's worth checking out. It's better to know for a fact than to guess.

Brakes aren't something you want to mix n match pieces and hope they work. Imo, it's worth checking and knowing if something is compatable and is designed to work together before you just rig it together.

Drums and discs operate differently. Their fluid pressure/ volume requirements are not the same. This is why it's critical to have the right components. This is why I would use the components from the disc car for the disc brakes.

Mgomez- The axle flanges (for mounting the brakes) are different on the disc rear axles than on the drum rear axles. You can't just bolt up the discs on the drum axle.

There's another post on here where a guy modified his drum rear housing to fit disc brakes, so it is possible to do (if you want to keep your original axle.) But, you have to dissassemble the axles out anyway to do this so it would be just as easy to use the disc brake axle since you already have it. (either install your gears in the disc brake housing, or just leave the disc housing assembled and bolt it in)

Again- before oyu start this- check the gear ratios between what you have now and the new one. If the new one is acceptable to you (They offered various ones throughout the years, both with posi and non posi)- then I'd pull the differential cover off and inspect inside. Any obvious broken pieces? check the fluid- is it very metallic? any obvious leaks around the axle seals or pinion seal? Install the cover and fill it back up (install posi lube if it's a posi rear). It's worth checking all this because the last thing you want to do is install parts that are worn out/ no good.

Assuming the disc brakes are good (rotors aren't grooved/ calipers not frozen and pads Ok) then swap it over. I would inspect and swap the master cylinder and proportioning valve from the disc brake car to work with the disc brakes, but, that's me.

And I'd still pull the other parts off the parts car. Even if I'm wrong and they are the same, then you have extra parts to use that won't cost you a dime in case the ones you have currently break on you.

But, before you believe either of us on which parts are the same or different- look it up in a GM parts book. Talk to the parts guy at your local GM dealer and have him look the parts up (as if you were to buy them) then see if there's different part #s for these. Then, you will know for sure.

Just my 2 cents

 

tuske, you're right in that there are 2 parts numbers, but GM consolidated the 2 later in the build run, meaning that they used just the disc MC for both. I had forgotted about the disc/drum flange difference. good catch.

i really think you'd be better off just swapping the whole rear and calling it good. it'd be easier, and like he said, the "fix" kit works. to do that, all you do is unbolt the suspension, and switch it out. (and that one brake line junction in the middle.) I've done it more time then i care to remember.

I just prefer PBR calipers, but hey..... use what you got if it's cheap and it works.

 

I appreciate all the insight. I don't plan on actually doing this for a few months but I wanted to get all my info straight before I did anything. Thanks.

 

May have been 89-92 PBR set-ups.

JamesC

 

When I get this new backing plate finished no mods to a drum flange will be needed. Keep your eyes peeled.

Ed

 

About the master cylinders:

https://www.thirdgen.org/forums/susp...fferences.html